1. Field of the Invention
The present invention relates to an illumination device using a light guide element and to an information processing apparatus provided with the illumination device.
2. Description of Related Art
The facsimile telegraphs, electronic photo copiers and other information processing apparatus are equipped with a reader for documents. The reader is associated with the illumination device in the form of a discharge tube such as fluorescent tube or an linear array of a great number of LED (light emitting element) chips.
In recent years, the facsimile telegraph and personal computer have widely spread. A peripheral device therefor, namely scanner, is coming into general home use. Along with this comes a growing demand for products of smaller size and lower price. To meet such a demand, the LED chip is favorable as the light source. To reduce the number of LED chips there have been previous proposals for making use of a light guide element in the form of a stick.
FIGS. 44 and 45 are respectively a perspective view and a side elevation view of the stick-shaped illumination device using the light guide element. An LED element 31 is used in combination with a light guide element 10 made from a light-transmissive substrate in the form of a quadrangular pole. Light from the LED element 31 enters the light guide element 10 at an entrance surface 12 thereof. As the substrate is propagating the light in the light guide element 10, a diffusion area 11 reflects or scatters the light to the outside of the light guide element 10. The diffusion area 11 is formed in a portion of the substrate by roughening one of its side surfaces or applying a light reflection coating thereto.
The LED element 31 is positioned adjacent the light guide element 10 so that all the entering rays from the entrance surface 12 to the inside of the light guide element 10 satisfy the condition of total reflection. Therefore, they undergo repeated inter-reflections between the side walls of the light guide element 10, thus propagating in its interior.
As the cycle of reflection is repeated, the rays eventually fall on the diffusion area 11, where they are reflected or scattered. All or some of the rays go to an exit surface 13 opposite to the diffusion area 11 and therefrom emerge to the outside, thus illuminating a desired position.
FIGS. 46(a), 46(b) and 46(c) show another LED illumination device using the stick-shaped light guide element disclosed in, for example, Japanese Laid-Open Patent Application No. Hei 6-217084.
The illumination device is shown in the side elevation view of FIG. 46(a) together with a manuscript on the position to be illuminated. FIG. 46(b) is a cross sectional view taken in a perpendicular plane of FIG. 46(a) to the paper. FIG. 46(c) is an end view as looked from the direction of arrow A of the illumination device.
To make uniform the strength of illuminance throughout the entire longitudinal length, provision is made in bringing the center of the LED element 31 out of coincidence with the normal line at the center of the short dimension or width of the diffusion area 11 as shown in FIG. 46(c).
The light reaching the diffusion area 11 directly from the light source, or the direct light, is thus reduced in the intensity. In turn, the proportion of the indirect light that at least once reflects from the other inner surfaces of the light guide element 10 than the diffusion area 11 is so much increased. Such an arrangement can propagate the entering light even farther away from the light source, producing an advantage of improving the longitudinal unevenness of illuminance over the fact that the illuminance is too high near the light source and becomes rapidly lower as the distance increases.
As far as the arrangement described above is concerned, for the near zone of the diffusion area to the light source, it is, however, in the prior art that the direct light is not yet much reduced in intensity to attain a desired uniformity of illuminance throughout the longitudinal length. Therefore, the application of such an illumination device is limited to low classes of products. When in application to the high class, an expensive correction circuit has to be used, because the electrical signals are obtained from a more uneven illuminance distribution than is required.
Another problem arises from the fact that, as mentioned before, ever increasing numbers of items of that information processing apparatus which necessitates the illumination device are spreading into general home use. So, an even more reduction of its size becomes inevitable. This trend is reflected to a demand for a further reduction of the size of the illumination device, too. If the light guide element of the illumination device is reduced in the cross sectional area according to such a demand, the unevenness of illuminance distribution worsens so much as not to be fit for actual use.
In more detail, the smaller the cross section of the light guide element is made in a similar figure, the shorter the distance from the LED element to a position at which the entering ray is for the first time incident on the inner wall at the equivalent angle becomes in proportion. So, the distance the light propagates to reach the diffusion area becomes extremely shorter, causing the illuminance to rise in the near zone to the LED element and become progressively lower toward the farther zones. Therefore, a problem arises in that the problem of the unevenness of illuminance becomes even more difficult to solve.
An object of the invention is to provide an illumination device which is amenable to the easy technique of minimizing the size and has a higher uniformity of illuminance distribution, and an information processing apparatus using the same.
As applied to the type of illumination device in which the LED light source is used in combination with the light guide element, another object of the invention is to improve the compact form of the illumination device.
In the illumination device of the type described above, when the lateral size is reduced, the difference in illuminance between the near zone to the LED light source and the farthest zone therefrom increases largely. It is, therefore, another object of the invention to solve such a problem of the unevenness of illuminance.
To achieve the above objects, in accordance with an aspect of the invention, there is provided an illumination device which comprises a light source and a light-transmissive light guide element having an entrance surface at which light from the light source enters the light guide element, a diffusion area which diffuses the light coming from the entrance surface and an exit surface at which the diffused light exits in a predetermined direction, wherein the light guide element is formed such that the entering light coming from the entrance surface of the light guide element is not made incident directly on at least a part of the diffusion area of the light guide element.
In accordance with another aspect of the invention, there is provided an illumination device which comprises a light source and a light-transmissive light guide element having an entrance surface at which light from the light source enters the light guide element, a diffusion area which diffuses the light coming from the entrance surface and an exit surface at which the diffused light exits in a predetermined direction, wherein a part of the light guide element is narrowed.
By using such a construction and arrangement of the constituent parts, it is made possible to reduce the size sufficiently, while still permitting a uniformity of illumination to be achieved at a high strength, and to provide an illumination device of low cost.
It is made also possible to condense the projected light beam to a desired width, while keeping the uniform illumination, and, therefore, to provide illumination devices of wide versatility.
In accordance with a further aspect of the invention, there is provided an information processing apparatus equipped with an illumination device which comprises a light source and a light-transmissive light guide element having an entrance surface at which light from the light source enters the light guide element, a diffusion area which diffuses the light coming from the entrance surface and an exit surface at which the diffused light exits in a predetermined direction, wherein the light guide element is formed such that the entering light coming from the entrance surface of the light guide element is not made incident directly on at least a part of the diffusion area of the light guide element.
In accordance with a still further aspect of the invention, there is provided an information processing apparatus equipped with an illumination device which comprises a light source and a light-transmissive light guide element having an entrance surface at which light from the light source enters the light guide element, a diffusion area which diffuses the light coming from the entrance surface and an exit surface at which the diffused light exits in a predetermined direction, wherein a part of the light guide element is narrowed.
In addition, according to the invention, it is possible to provide an information processing apparatus capable of reading images with high accuracy and reliability.
These and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.